This invention relates generally to an infrared laser target that provides for critical detection of the infrared beam from a surveying transmitter. for indoor Global Positioning System (hereinafter G.P.S.), and more specifically to a mask overlay for an infrared target assembly that provides for precise work area settings within +/−0.0005 inch or less.
Targets with closely located mask overlays, for use in photogrammetry and automated theodolite systems have been available for years. Generally, of more current usage, the present invention incorporates the Global Positioning System or G.P.S., only on an indoor scale, as an optional method to precisely set various industrial devices and industrial equipment, including machinery and for close tolerance industrial surveying, as used in manufacturing and assembly operations. Normally, infrared targets without the mask overlay only have tolerances within several thousandths of an inch, which may be insufficient to obtain the precision required in a machining operation, the manufacturing of parts necessary for particular industries, or industrial surveying. Additionally, laser scanners emit a laser beam along a line. That laser line represents the position of an edge used in a step of manufacturing, such as the position of a composite lay up sheet.
For reference, retro-reflective photo targets, with a mask overlay have had countless design adaptations to enhance precision for the various settings and component features that are measured using close range industrial photogrammetry. These adaptations may include straight holes, threaded holes, surfaces, edges, slots and the like. The prior art frequently obtains tolerances in the vicinity of 0.0005 inch.
Currently, most targets, for the photogrammetric methods and systems generally use a 3M® type tape material that has small glass beads coated onto its top surface, with a reflective coating on the back side of the beads, and integral with the tape. When the strobe light from the photogrammetric camera fires, it causes the glass beads on the tape to reflect the light and thereby creates spots of light that appear on a photograph. The spots are then measured for three-dimensional locations in the X, Y and Z axes.
Commonly some targets, as used in photogrammetry, serve as reference points, without achieving a critical X, Y and Z location. These types of targets may be simply an adhesive strip upon a machine or item to be surveyed.
However, many targets require critical dimensions and are mounted upon a close tolerance steel body that supports the target. These are generally called hard body targets. The intention is for the retro-reflective target to be located quite precisely in three dimensions on the body which in turn usually represents an X, Y and Z value of the machine or item being positioned or surveyed. The 3M® retro-reflective material is adhered to a tape product of a known definite thickness, the material being covered with small glass beads of approximately 0.003 inch diameter. This material has a granular appearance similar to that of grit on sandpaper.
The beads are 0.003 inch in diameter but, in many machining operations, the tolerance of the target dot location must be +/−0.0005 inch or less. As a result, the components of the standard materials without a mask overlay make it impossible to meet the tolerances required.
To accomplish the final close tolerance that complies with job requirements, some industries use a mask overlay that is critically located in two directions, and a third critical location is the surface of the 3M® material that adheres to the tape and compensates for the thickness of the material used. The final application of the mask overlay produces an area of reflectivity that is controlled by size, roundness, crispness, clarity and critical location in relation to the target body.
As can be seen in the prior art and in U.S. Pat. No. 5,073,005, to Hubbs, obtaining greater precision through the usage of a mask overlay, applied over a target, and a mask that may have a reflective member applied upon it, can attain precise locations, generally within 0.001 inch tolerance or less. This occurs through the use of a mask that has a finite aperture that allows the entrance of the light from the camera strobe therethrough, and adds precision to the establishment of the X, Y and Z axes when such a surveying instrument, applying photogrammetry, is used.
This new invention also uses a mask overlay and a reflective ring but operates within a system of multiple transmitters mounted and secured high inside of a manufacturing facility somewhat similar to orbiting satellites. These transmitters send out an infrared signal beam, recognized by one or more detectors and then later emit a laser beam from a scanner. One type of detector is the flat detector, which is available from Arc Second, of Dulles, Va., which owns the indoor G.P.S. measurement system. The prior art flat detector target assemblies have an engraved mask proximate to the lens.
Sometimes, the detector has no critical X, Y, Z values, and may be used simply as a reference, possibly to detect movement. However, like the hard body photo target, there is a need for a target assembly that has definite close tolerance X, Y, Z values. This accurate target can then interface with other features on items being measured or monitored such as straight holes, threaded holes, surfaces, edges and others. An example of such a target requirement is from Bombardier, Inc. of Montréal, Québec. Again, like the photo target, the hard body target takes many forms.
The goal of this invention is to produce an infrared laser target that represents X, Y, Z values within a tolerance of approximately +/−0.0005, or finer. We reach this goal by applying the mask overlay and the reflective ring to the target. The mask overlay locates the target precisely via the infrared beam of the G.P.S. The reflective ring then allows a laser scanner to establish a known line from the target previously located. The current design consists of multiple components, some having close tolerance assembly features. The difficulty of manufacturing multiple components with very close tolerances is that variations or tolerances stack up, or accumulate, during assembly of a target which jeopardizes the goal of a final target at a location within a 0.0005 inch or less tolerance.